This invention relates to a process for preparing cellulose ethers, particularly to a process of preparing mixed hydroxyalkylcellulose ethers.
In the preparation of cellulose ethers, substituent groups can often become attached to the cellulose molecule in various ways. For example, each repeating unit of the cellulose molecule contains one primary and two secondary hydroxyl groups all of which may be converted to ether groups. The properties of diverse cellulose ethers having similar amounts and types of substituent groups often vary depending on which of these hydroxyl groups become substituted.
When a cellulose ether having hydroxyalkyl substituents is prepared, the introduction of a hydroxyalkoxyl group to the cellulose molecule creates a new hydroxyl group which can itself be substituted. Thus, poly(alkylene oxide) chains often form in the preparation of hydroxyalkylcellulose ethers. Again, the properties of the cellulose ether will vary, often substantially, depending on how uniformly the hydroxyalkoxyl substituent group is distributed through the molecule. Because the formation of such side chains is generally random and unpredictable, it is difficult to obtain a hydroxyalkylcellulose ether wherein the hydroxyalkoxyl substituents are distributed relatively uniformly through the molecule. When mixed hydroxyalkylcellulose ethers are prepared, it is especially difficult to obtain uniform distribution of the hydroxyalkoxyl substituents throughout the molecule. It would, therefore, be desirable to have a process wherein mixed hydroxyalkylcellulose ethers are prepared having hydroxyalkoxyl substituents which are relatively uniformly distributed throughout the cellulose molecule.